1. Field of the Invention
The present invention relates to a toner and to a development agent, an image forming apparatus, and a process cartridge that use the toner.
2. Description of the Background Art
Latent images formed electrically or magnetically are typically rendered visible by an electrophotographic image forming apparatus using toner (electrophotographic toner).
For example, in electrophotography, electrostatic images (latent images) are formed on an image bearing member (typically a photoreceptor) and developed with toner to form visible toner images. The toner image is then transferred onto a transfer medium, typically paper, and thereafter fixed thereon. In the process in which the toner image is fixed on the transfer medium, a thermal fixing device such as a heating roller fixing system or a heating belt fixing system is generally used for better energy efficiency.
In recent years, demand for ever faster, more energy-efficient image forming apparatuses has continued to grow. Toner having excellent low-temperature fixing properties and providing quality images is one of the keys to satisfying such demand.
To attain a toner having excellent low-temperature fixing, binder resins forming the toner are required to have low softening temperatures. However, when the softening temperature of the binder resin is low, part of the toner image tends to adhere to the surface of the fixing device when fixing the image and transferring the image onto the transfer medium (so-called offset, also referred to as hot offset). In addition, the ability of the toner to withstand high temperatures without decomposing also deteriorates, leading to clumping (in which the toner particles stick to each other) under high-temperature conditions in particular.
Furthermore, there are other problems, such that the toner particles adhere to the inside of a development device or to carrier particles, thereby contaminating the development device or causing filming on the surface of the image bearing member.
To solve these problems, use of crystalline resins as the binder resins for toner is known. Crystalline resins quickly soften at their melting points so that it is possible to lower the softening point of the toner to around its melting points while securing excellent high-temperature stability at the melting points or temperatures lower than that. Therefore, such toner canhfittin have a good combination of low-temperature fixing and high-temperature stability.
For example, Japanese Examined Patent Application Publication Nos. H04-24702 (JP-H04-24702-A) and JP-H04-24703-A describe toners using crystalline resins elongated from a crystalline polyester by diisocyanate as the binder resins. These toners have excellent low-temperature fixing properties but insufficient hot offset resistance, which is not satisfactory in terms of the level of quality currently required.
In addition, Japanese Patent No. 3910338 (JP-3910338-B) describes toner that uses crystalline resins having a cross-linked structure by unsaturated linking containing a sulfonic acid group and can overcome hot offset. Further, Japanese Patent Application Publication No. 2010-77419 (JP-2010-77419-A) describes regulating the ratio of the softening point to the peak temperature of the melting heat and viscoelasticity to obtain an excellent combination of low-temperature fixing and high-temperature stability.
However, these toners having crystalline resins as the main component of their binder resins, although they have excellent impact resistance, also exhibit poor indentation hardness and scratch hardness. As a consequence, images output with such toners are vulnerable to abrasion such as scratching and rubbing.
JP-3360527-B describes regulating the durometer hardness of crystalline resins in the toner and including inorganic particulates in the toner to improve the stress resistance of the toner. However, the abrasion resistance of the output image is not improved. In addition, the fixing properties worsen due to the inorganic particulates, thereby degrading the low-temperature fixing of the crystalline resin